1. Field of the Invention
The invention pertains to an improved in-line fluid operated motor coupled to an injection pump for injecting predetermined quantities of secondary fluid into a primary fluid stream.
2. Background of the Prior Art
Fluid powered motors have been know in the prior art for driving a pump connected to a source of fluid additives. A fluid powered motor installed in a line containing primary fluid reciprocates to draw a quantity of secondary fluid into the primary fluid with each reciprocation. Such devices have been applied to add medication to drinking water for poultry and livestock, treat water with additives, add fertilizer concentrate to irrigation water, or add lubricant or cleaning agents to water.
In conventional reciprocating fluid power motors, a sliding shaft extends through the head of a differential stepped piston, usually through the center of the piston and extends on both sides of the piston face. The shaft is connected to some snap over center or toggle mechanism to control two sets of "poppet" valves which alternately open and close fluid passages in a one stepped piston face or in two stepped piston faces. When the piston moves up or down in response to high pressure on one side of the stepped face, an end of the rod strikes the housing and causes the rod to stop moving while the piston continues to move. This causes a relative sliding movement between the rod and the pressurized face of the piston which requires a seal to prevent loss of pressure.
Newer designs, such as the one disclosed in U.S. Pat. No. 5,137,435, have eliminated the need for a sliding seal between a shifting mechanism and the upper face of the stepped piston, but there is still a need for compressing a strong spring in a snap-over center mechanism to insure that sets of valves in each face of the piston are shifted. There is a fluid pressure induced force on the poppet valves of the closed face of the piston which must be overcome by the shifting mechanism to shift the poppet valves. A large amount of energy is stored in compressed springs which drives a valve shifter in a snap-over center action. Although considerably better than older designs which employ springs which are stretched in tension, there is still considerable noise produced which is objectionable in certain installations. A case in point is the installation of such a unit in a home sprinkling system where the reciprocating unit is placed in close proximity to a bedroom. There is still enough noise to wake certain people when the unit winds the springs, then suddenly drives the valves to the opposite position to change the direction of reciprocation. There is still undesirable excessive wear and tear because of the required high driving force of the shifting mechanism applied to working parts. If the springs are too weak or too small, the unit will not reliably shift at all. It would be desirable to produce an in-line fluid pressure operated motor which does not require a snap-over center shifting mechanism to reverse the valve orientation.
Such a reciprocating fluid powered motor is used to drive an injection pump. An injection pump is connected to the reciprocating motor housing. It has an inlet leading to a source of secondary fluid. Prior art injection pumps rely on too many sliding seals which wear out too rapidly if the secondary fluid contains abrasive particles. Some prior art injection pumps can be adjusted to deliver a greater or lesser quantity of secondary fluid per reciprocation, but adjustment requires the use of tools to disassemble the pump and require too much time to make the adjustment. They often produce an unreliable or unknown quantity of injected fluid. It would be desirable to have an improved injection that can be disassembled easily, reduces reliance on sliding seals which can wear in contact with an abrasive fluid, is self-priming, draws in excess fluid, and is reliably and predictably adjustable.